1. Technical Field
The present invention relates to internal combustion engines and their related exhaust emissions. More specifically, the present invention discloses a method for reducing harmful and toxic exhaust gases from an internal combustion engine having at least one cylinder supplied with an air/fuel mixture when a crankshaft of the internal combustion engine is rotated.
2. Background Information
In internal combustion engines it is desirable to reduce the harmful and toxic substances that occur in the exhaust gases of the internal combustion engine in order to reduce the burden on the surrounding environment, as well as comply with the legal requirements placed on internal combustion engines. Substances that are found in exhaust gases include carbon monoxide (xe2x80x9cCOxe2x80x9d), hydrocarbons (xe2x80x9cHCxe2x80x9d) and nitrogen oxides (xe2x80x9cNOxxe2x80x9d).
In order to reduce these substances from the exhaust gases, the internal combustion engine is provided with a catalyzer or catalytic converter that chemically converts these substances to those which do not adversely affect the surrounding environment. However, this chemical reaction occurs only when the catalytic converter has reached a predetermined working temperature, which is reached after a predetermined running time of the internal combustion engine. Therefore, when cold-starting the internal combustion engine, no reduction of the toxic substances takes place in the catalytic converter.
Another problem that occurs when cold-starting internal combustion engines is that a relatively large amount of fuel in relation to the supplied air, i.e., a rich air/fuel mixture, must be supplied to the internal combustion engine in order for the internal combustion engine to be able to start and to be able to operate at a substantially constant rotation speed during idling. This rich air/fuel mixture is also supplied so that the internal combustion engine will be able to provide an increased torque upon acceleration. As such, running of the internal combustion engine is guaranteed before the internal combustion engine has reached its operating temperature.
The absence of the exhaust gas cleaning by the catalytic converter and the rich air/fuel mixture means that the levels of CO, HC and NOx emitted from the internal combustion engine are high upon cold-starting of the internal combustion engine. Attempts have previously been made to reduce the fuel quantity in relation to the air supplied, i.e., drive the internal combustion engine with a leaner air/fuel mixture upon cold-starting. However, this results in the internal combustion engine working very unevenly during idling, and a poor drivability of the internal combustion engine. The reason why rotation speed varies during idling is that the internal combustion engine torque is very sensitive to variations in the lambda value of the air/fuel mixture supplied to the internal combustion engine cylinder space when the air/fuel mixture is lean. The lambda value, or the air excess coefficient as it is also called, is the actual amount of air supplied divided by the amount of air theoretically necessary for complete combustion. If the lambda value is greater than one, the air/fuel mixture is lean; if the lambda value is less than one, the air/fuel mixture is rich.
It is possible to carefully control the fuel supplied from a fuel injection valve with the aid of the internal combustion engine fuel injection system, thereby obtaining a substantially constant lambda value for the air/fuel mixture supplied. However, when the internal combustion engine is cold, fuel condenses on the comparatively cold walls in the intake channel and in the cylinder. The fuel condensed on the walls evaporates during idling, following the air/fuel mixture that flows into the intake channel and is supplied to the cylinder space. If the evaporation of the fuel condensed on the walls is uneven, for example, on account of pressure changes, temperature gradients or the flow velocity of the air/fuel mixture in the intake channel, there will be a variation in the lambda value of the air/fuel mixture supplied to the cylinder space.
Since the torque provided by the internal combustion engine varies during idling upon a cold start, the rotation speed of the internal combustion engine also varies. The rotation speed of the internal combustion engine here means the crankshaft rotation speed of the internal combustion engine. When the rotation speed varies, the pressure in the intake channel also varies, which in turn leads to the evaporation of the condensed fuel varying so that there is a variation in the lambda value of the air/fuel mixture supplied to the cylinder space. The uneven rotation speed of the internal combustion engine is thereby intensified.
The present invention reduces harmful and toxic exhaust gases from an internal combustion engine upon cold starts. Further, the present invention allows an internal combustion engine to operate with a substantially constant rotation speed upon idling when a lean air/fuel mixture is supplied to the internal combustion engine.
This is achieved by the present invention with a method comprising supplying an air/fuel mixture with a lambda value of greater than one to the cylinder, and controlling the pressure in the intake channel by means of an electric motor/generator coupled to the crankshaft, so that when the pressure in the intake channel exceeds a predetermined pressure, the electric motor/generator is controlled so that the pressure in the intake channel can decrease, and when the pressure in the intake channel falls below a predetermined pressure, the electric motor/generator is controlled so that the pressure in the intake channel can increase.
By controlling the pressure in the intake channels of the internal combustion engine with the aid of an electric motor/generator, the pressure in the intake channels can be maintained substantially constant. The lambda value of the air/fuel mixture supplied to the cylinders is thus maintained substantially constant, meaning that the torque provided by the internal combustion engine is substantially constant. The rotation speed of the internal combustion engine will also be substantially constant, meaning that harmful and toxic exhaust gases, particularly hydrocarbons, from the internal combustion engine decrease.